This invention relates to an optical switching device including multiple quantum wells; and, in particular, to a self-electrooptic effect device having a multiple quantum wells region, a optical bistable switching device made thereof and a novel process for the manufacture thereof.
A wide range of recent research effects have achieved the development of semiconductor optical bistable switches capable of high speed switching, free space interconnection and simultaneous parallel processing of signals. These switches contain a semiconductor quantum wells region having an electric contact point as a self-electrooptic effect device. Operation of such optical switches is performed through a change in the light absorption characteristics in response to a change in applied electric field. This is mainly due to a quantum confined stark effect(QCSE) existing in a semiconductor quantum wells region.
The structure of multiple quantum wells made of, for example, multilayers of GaAs/AlGaAs and the above-mentioned QCSE phenomenon are described in an article by T. H. Wood et al., High-speed Optical Modulation with GaAs/AlGaAs Quantum Wells in a p-i-n Diode Structure, Appl. Phys. Le 44, 16(1984), and an article by David A. B. Miller et al., The Quantum Well Self-Electrooptic Effect Device: Optoelectronic Bistability and Oscillation, and Self-Linearized Modulation, IEEE J. of Quantum Electronics, QE-21, 1462(1985). The quantum wells disclosed in these articles are grown by the so-called molecular beam epitaxy (MBE) method, which has been used for the preparation of optical devices or microwave devices. The MBE technique is, however, inferior to a more recently developed method called metal organic vapor phase epitaxy(MOVPE) technique because the MBE process requires a higher level of vacuum and is of a lower production rate even though it has the advantage of easier control on the impurity concentration or composition ratio of a mixed crystal through a manipulation of certain parameters.
As the demand for optical switching devices is growing rapidly, various MOVPE techniques have been tried for very large scale production in the future. Self-electrooptic effect devices prepared by using the MOVPE method are disclosed in an article by M. Whitehead, et al., Quantum Confined Stark Shifts in MOVPE-Grown GaAs-AlGaAs Multiple Quantum Wells, Electronics Letters, 23, 1048 (1987), and also in an article by H. C. Lee, et al., IEEE J. of Quantum Electronics, 24, 1581(1988). The self-electrooptic devices disclosed in these articles show a similar QCSE as the devices prepared by using the MBE method, but fail to show a negative resistance, i.e., decrease in light absorption in response to the applied electric field, which is necessary for a self-electrooptic effect device to be useful as an optical switching device.